1. Field of the Invention
The present invention relates generally to a laboratory device for growing microorganisms in liquid cultures in a multi-compartment format, which provides convenience for dispensing, inoculation, incubation and harvesting.
2. Prior Art
Simultaneous cultivation of a large number of microorganisms in laboratory conditions is common practice in microbiology for exploration of useful microbial activities and products. Conventionally, shake flasks, test tubes and petri dishes are used as the culturing devices. When these conventional devices are used, a separate unit must be used for each microorganism in each growth medium and each unit has to be handled individually throughout the culturing process. In a typical culturing process involving the conventional devices, such as shake flasks for example, a technician must dispense growth medium into each flask, sterilize the medium in flasks by autoclaving, inoculate each flask with a test sample, incubate the flasks on a mechanical shaker and harvest the liquid cultures for testing. This conventional culturing process is tedious, labor intensive and time consuming, particularly when it involves a large number of microorganisms, and it is often the bottleneck in the process of exploration of microorganisms in many microbiology laboratories.
To date, the prior art has provided several devices useful for culturing microorganisms, which simplify some steps of the conventional culturing process. Typically, multi-compartment devices are found to be easier and quicker to use than the conventional single compartment devices. For example, U.S. Pat. No. 3,960,658 discloses a multi-medium petri dish that comprises a petri-type dish where the base is divided into separate compartments for containing different culture media. Similarly, U.S. Pat. No. 4,012,288 describes a tissue culture cluster dish having a removable lid and a base with multi-wells formed therein. Each of the wells in the cluster dish can be used for one medium or one sample, and therefore, multi-wells in a single cluster dish can be used to host several media or samples at the same time. These multi-compartment cluster devices significantly reduce the need of handling each of individual petri dishes.
A problem associated with the use of such cluster devices is the greater chance of contamination of the device from outside environments when lids are removed for dispensing liquid media and inoculation. One approach to the problem is seen in U.S. Pat. No. 5,817,510 that discloses a cluster dish with a lid having a plurality of channels radiated from a central positioned aperture. Each of the channels extends through the lid to be positioned above each well in the base. Through the channels, liquid media and target microorganisms can be introduced into each of the wells without removing the lid, thereby reducing the chance of contamination. U.S. Pat. No. 3,769,936 discloses a petri dish cover with an orifice that may be opened or closed for dispensing media and inoculation without removing the lid. This approach is adapted to cluster devices as seen in U.S. Pat. No. 5,817,510. Although the lids with access orifices for cluster dishes are useful to reduce contamination during liquid communication, they do not provide any easiness or convenience for dispensing and inoculation because each well in a cluster device must be accessed individually. In no such cluster device or system in prior art, does it appear that all the wells can be accessed simultaneously and equally for the purpose of liquid communication.
A common feature of the multi-well cluster devices disclosed in prior art is that the lid and the base are constructed so that when in place on the base, a gap is created between the lid and the base. This feature not only permits air exchange between the inside and the outside of the devices, but also exposes all the wells to the same internal atmosphere. The feature, however, becomes a problem when liquid cultures are used because of possible cross contamination between the wells. Such cross contamination can occur as a result of the transfer of condensed moisture on the inner surface of the lid cover from one well to any other well or as a result of spills during handling. U.S. Pat. No. 4,012,288 discloses the use of circular ridge on the lower surface of the lid over the top of each well. The circular ridge on the lid can reduce the cross contamination caused by condensed moisture, but it does not prevent spills.
Another concern in using these open-lid cluster devices is safety. Because the gap allows air movement between the inside and the outside of the device without filtering, air-dispersible microorganisms (e.g. Aspergillus species produce air-dispersible spores) grown inside these devices can easily escape from these devices to contaminate the outside environment. Contamination is a primary concern in the practice of industrial exploration of microbial products from nature, which often involves cultivation of unknown microorganisms collected from diverse environments.
Several methods are known in prior art that may be used to provide a sealed environment for culturing microorganisms. One of them is the use of air-permeable plastic film. An example of such use is the bags made from air permeable plastic film for cultivating eatable mushrooms as described in U.S. Pat. Nos. 4,311,477, 4,878,312, 4,977,702, 5,662,576 and 5,659,997. In analogous fashion, air-permeable plastic film has been used in thin film culture plates for laboratory applications as disclosed in U.S. Pat. Nos. 4,565,783, 5,089,413, 5,232,838 and 5,869,321. A typical thin film culture plate comprises a waterproof substrate as the base coated with a gelling and a transparent, air-permeable cover film adhered to the upper surface of the gelling medium. Upon inoculation of the thin film plates, microorganisms will grow on the surface of the gelling medium under the air-permeable cover film. Other culturing devices involve airpermeable plastic film are disclosed in U.S. Pat. Nos. 5,693,537 and 5,714,384.
Most of microorganisms encountered in microbiology practice are aerobic microorganisms that often grow exclusively on the surface of the culture medium that exposes to air. For example, when cultured in petri dishes, most of microorganisms grow on the upper surface of the medium that faces the lid rather than on the lower surface that is in contact with the base of the petri dish. Similarly, the multi-compartment cluster devices known in prior art are designed for culturing microorganisms on a single surface of the medium. A disadvantage of such design is the relatively small area, often less than 50%, of the internal surface of the compartments being used for growth. With the conventional flasks and test tubes, microbiologists often use rotary shakers to increase the surface area and oxygen transfer for growth. The existing multi-compartment cluster devices, however, are unsuitable for use on shakers because of spills and cross contamination between compartments. Therefore, the surface area available for growth in multi-compartment cluster devices is restricted to the physical size of the compartments. In addition, the culturing methods involving shakers are not suitable for microorganisms that require a solid surface to attach and grow on.
One method to increase the surface area between air and liquid medium known in prior art is the use of highly porous plastic substrates such as sponges or foams. A good example of the effective use of such method is in biological digestion of nutrients in wastewater treatment as disclosed in British Pat. No. 2,006,181B and in Canadian Pat. No. 1,055,169. A typical plastic substrate suitable for culturing microorganisms is the flexible polyurethane foam described in U.S. Pat. Nos. 4,503,150 and 4,689,301 and in the report "Production of sulphated polysaccharides by a biophotoreactor having immobilized Porphridium cruentum cells" in Academie des Sciences, 1981, vol. 293, series III, pp. 35-37.